Tear-resistant biodegradable copolyester as well as preparation method and application thereof

Abstract

The invention discloses a tear-resistant biodegradable copolyester as well as a preparation method and application thereof, the preparation method comprises the following steps: 1) mixing adipic acid, terephthalic acid, 1, 4-butanediol and diethylene glycol, and carrying out polymerization reaction to obtain an oligomer; and 2) mixing the oligomer with a reinforcing agent, and carrying out condensation polymerization to obtain the biodegradable copolyester. And fully mixing the copolyester with fillers such as calcium carbonate and polylactic acid, extruding, and blowing to obtain the biodegradable film. The biodegradable film prepared by the invention has excellent strength and tear resistance, and can be widely applied to the field of film bags.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials, specifically to a high-strength, tear-resistant biodegradable copolyester, its preparation method, and its applications. Background Technology

[0002] Biodegradable plastics have already replaced traditional non-degradable general-purpose plastics in many fields, alleviating "white pollution" on land to some extent. Among them, polybutylene terephthalate (PBAT) is undoubtedly one of the most popular materials due to its excellent comprehensive performance and wide range of applications. PBAT can be completely degraded through composting, but its degradation in seawater is very limited. Adding hydrophilic monomers such as diethylene glycol can improve its degradability in seawater and also provide good tensile strength. However, when PBAT copolymers with added hydrophilic monomers are blended with fillers such as mineral powder, the tensile properties, impact resistance, and tear resistance of the film are significantly reduced, resulting in easy breakage under load and easy cracking during tearing in downstream applications. Therefore, creating a PBAT biodegradable material with good degradability in seawater and high strength and tear resistance is extremely crucial. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a high-strength, tear-resistant, biodegradable copolyester, its preparation method, and its applications. Research has shown that glycidyl-based polyol amine reinforcing agents can be added during the polymerization stage of PBAT-modified copolyester, significantly improving the tensile strength, impact strength, and tear strength of the polyester film / bag, thus expanding the downstream application areas of biodegradable polyester.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a tear-resistant, biodegradable copolyester, characterized by comprising the following steps:

[0006] 1) Adipic acid, terephthalic acid, 1,4-butanediol, and diethylene glycol are mixed and polymerized to obtain oligomers;

[0007] 2) Mix the oligomer with the reinforcing agent and carry out a polycondensation reaction to obtain a biodegradable copolyester.

[0008] In some preferred embodiments of the present invention, in step 1), the ratio of the total molar amount of 1,4-butanediol and diethylene glycol to the total molar amount of adipic acid and terephthalic acid is 1.1-2.0:1.0.

[0009] In step 1), the molar ratio of 1,4-butanediol to diethylene glycol is 1.0-4.0:1.0; and / or,

[0010] The molar ratio of adipic acid to terephthalic acid is 0.5-1.5:1.0.

[0011] Preferably, in step 1), the reaction temperature is 170-250℃ and the reaction time is 1-5h.

[0012] Preferably, in step 1), a catalyst is also added. Preferably, the amount of catalyst added is 0.1%-0.5% of the total mass of the reaction raw materials in step 1).

[0013] Preferably, in step 1), the catalyst is a titanium-based catalyst, preferably a titanate ester, which can be selected from any one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, tetrabutyl titanate, and tetraisooctyl titanate.

[0014] Preferably, the number-average molecular weight of the oligomer is 500-4000 g / mol.

[0015] Preferably, in step 2), the mass of the reinforcing agent added is 0.1%-1.0% of the total mass of the raw materials.

[0016] Preferably, in step 2), the reinforcing agent is glycidyl polyol amine.

[0017] Preferably, the glycidyl polyol amine is prepared by reacting glycidyl ether and polyol amine.

[0018] Preferably, the glycidyl ether is selected from one or more of 1,4-butanediol diglycidyl ether, glycerol triglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether, with 1,4-butanediol diglycidyl ether being the most preferred.

[0019] Preferably, the polyol amine is selected from one or more of diethanolamine, N-methyldiethanolamine, triethanolamine, triisopropanolamine, diisopropanolamine, and N-butyldiethanolamine, with diethanolamine being preferred.

[0020] The solvent is a diol, which may be selected from one or more of ethylene glycol, 1,4-butanediol, and diethylene glycol, preferably 1,4-butanediol.

[0021] The mass ratio of the glycidyl ether to the polyol amine is 1:1-3.

[0022] Preferably, the reaction between the glycidyl ether and the polyol amine is carried out in a solvent, and the amount of solvent added is 5-10 times the mass of the glycidyl ether.

[0023] The reaction temperature of the glycidyl ether with the polyol amine is 50-60℃, and the reaction time is 2-5h.

[0024] In step 2), the polycondensation reaction pressure is 10-500 Pa, the reaction temperature is 220-280 ℃, and the reaction time is 1-5 h.

[0025] The present invention also provides the application of the copolyester in the preparation of biodegradable membranes.

[0026] A biodegradable membrane comprising the following raw materials in parts by weight:

[0027] 50-70 parts copolyester

[0028] 20-30 parts calcium carbonate

[0029] 5-10 parts of polylactic acid

[0030] 0-2 parts of opening agent

[0031] 0-1 part compatibilizer.

[0032] The copolyester mentioned is a copolyester prepared using the preparation method described in this invention.

[0033] Preferably, the calcium carbonate has a fineness of 1000-8000 mesh, more preferably 3000-6000 mesh.

[0034] Preferably, the opening agent can be selected from one or more of stearamide, erucamide, and oleamide, with erucamide being preferred.

[0035] Preferably, the compatibilizer may be selected from one or more of hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and isoflurone diisocyanate, with hexamethylene diisocyanate being the most preferred.

[0036] The preparation method of the biodegradable membrane is as follows: after fully mixing copolyester with calcium carbonate, polylactic acid, optional opening agent and optional compatibilizer, the mixture is extruded and blown into a film to obtain a biodegradable membrane.

[0037] Preferably, the extrusion temperature is 150-200℃ and the extrusion speed is 200-500rpm.

[0038] Preferably, the blown film is made using a blown film machine, with a screw temperature of 150-200℃ and a traction speed of 10-30m / min.

[0039] In some preferred embodiments of the present invention, the number-average molecular weight of the biodegradable membrane is 2 × 10⁻⁶. 5 -8×10 5 The melt index is 1-10 g / 10 min at 190℃ and 2.16 kg.

[0040] In the preparation of PBAT resin, this invention introduces glycidyl polyol amines as reinforcing agents into the polymerization reaction. First, the reinforcing agent containing polyfunctional hydroxyl groups can act as branching points to promote the reaction, improve production efficiency, and form a polymer with a three-dimensional structure, thereby improving the tensile strength and tear resistance of the copolyester. Second, after PBAT is modified with diethylene glycol, the crystallinity of the copolyester decreases significantly, resulting in lower impact strength. The introduction of amino groups can form hydrogen bonds with ester groups, enhancing intermolecular forces, promoting copolyester crystallization, and compensating for the inherent performance problems of the copolyester. In addition, glycidyl polyol amines can also combine with free terminal carboxyl groups generated by thermal degradation, reducing the acid value of the product and improving shelf life.

[0041] This invention effectively improves the mechanical properties of copolyester film bags by introducing glycidyl-based polyol amines as reinforcing agents during the polymerization process of PBAT-modified copolyester.

[0042] In some preferred embodiments of the present invention, the tear resistance is >3000mN, the dart impact resistance is >250g, the tensile strength is >50MPa, and the tensile modulus is >100MPa, to meet the application requirements of downstream membrane bags. Detailed Implementation

[0043] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0044] In the following embodiments of the present invention, the raw materials include adipic acid (Zhejiang Liaohua), terephthalic acid (Yangzi Petrochemical), 1,4-butanediol (Xinjiang Meike), diethylene glycol (Shanghai Petrochemical), modified additives calcium carbonate (Foshan Taidi Chemical), polylactic acid (Anhui Fengyuan), catalysts tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, tetraisooctyl titanate, tetrabutyl titanate, opening agents erucamide and oleamide, compatibilizers hexamethylene diisocyanate and isoflavone diisocyanate, all of which were purchased from Inokai Reagent Network. Unless otherwise specified, the remaining raw materials are also commercially available.

[0045] The reinforcing agent, glycidyl polyol amine, needs to be prepared in-house. The specific preparation method is as follows:

[0046] (1) In a four-necked flask equipped with a stirring and condensing device, add 10g of 1,4-butanediol diglycidyl ether, 20g of diethanolamine and 70g of 1,4-butanediol respectively, heat to 60℃, and react for 3h to obtain enhancer A.

[0047] (2) In a four-necked flask equipped with a stirring and condensing device, add 10g of 1,4-butanediol diglycidyl ether, 20g of N-methyldiethanolamine and 70g of ethylene glycol respectively, heat to 60℃, and react for 3h to obtain enhancer B.

[0048] (3) In a four-necked flask equipped with a stirring and condensing device, add 10g of diethylene glycol diglycidyl ether, 10g of triethanolamine and 80g of diethylene glycol respectively, heat to 60℃, and react for 3h to obtain enhancer C.

[0049] The main processing equipment involved in this embodiment of the invention is as follows:

[0050] a) Twin-screw extruder: Coperion, model ZSK 26Mc 18, length-to-diameter ratio of 52, screw diameter of 26cm;

[0051] b) Film blowing machine, Zhangjiagang Lianjiang Machinery Co., Ltd., model SCM 25, length-to-diameter ratio of 30, screw diameter of 25cm.

[0052] The main testing methods involved in this embodiment of the invention are as follows:

[0053] a) Relative molecular mass: The relative molecular mass of the polymer was determined using Waters gel chromatography with chloroform as the mobile phase, an elution rate of 1 mL / min, a temperature of 40 °C, and narrow-distribution polystyrene as the standard sample.

[0054] b) Melt flow index: The melt mass flow rate (MFR) was measured using a GOTTFERT melt flow index tester at 190°C and 2.16 kg.

[0055] c) Acid value: Performed according to Method A of GB / T 14190-2008. The mixed solvent used is phenol-chloroform, with a volume ratio of 2:3. The standard titration solution is potassium hydroxide-benzyl alcohol, with a concentration of 0.01 mol / L, and bromophenol blue indicator concentration of 0.2%. Sample preparation: Dissolve 0.5 g of sample in 25.00 mL of the phenol-chloroform mixed solvent;

[0056] d) Tear strength: Tested using an Elmender tear tester (model TMT83-76) according to standard GB / T 16578. At least ten samples were used in each group, and the average value was taken.

[0057] e) Dart impact: The test was conducted using a dart impact tester, model Ray Ran FD-A2, in accordance with the standard GB / T 9639.

[0058] f) Tensile properties: The test was conducted using a universal tensile testing machine, referring to standard ISO 527-3:2018. First, the film sample was cut into rectangular strips (150mm×15mm) with a cutter, and then clamped on a single-column tensile testing machine (Zwick, Z0.5) with a gauge length of 50mm. The tensile properties were tested using a tensile force of 200N at a speed of 500mm / min, and the data was transmitted to the computer through a sensor. Five measurements were taken and the average value was taken.

[0059]

Example 1

[0060] 1) Mix 146g adipic acid, 332g terephthalic acid, 148.5g 1,4-butanediol, and 174.9g diethylene glycol, then add 0.8g tetramethyl titanate. After reacting at 250℃ for 2h, an oligomer is obtained with a number-average molecular weight of 2359g / mol.

[0061] After mixing the oligomer with 0.8 g of reinforcing agent A, the reaction pressure was gradually reduced to 10 PaA, and the mixture was reacted at 230 °C for 5 h to obtain a biodegradable copolyester with a number-average molecular weight of 2.5 × 10⁻⁶. 4 g / mol, melt index is 8.7 g / 10 min;

[0062] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3055mN, a dart impact strength of 258g, a tensile strength of 53MPa, and a tensile modulus of 113MPa.

[0063]

Example 2

[0064] 1) 233.6g adipic acid, 332g terephthalic acid, 280.8g 1,4-butanediol, and 165.4g diethylene glycol were mixed, and 2.02g tetraethyl titanate was added. After reacting at 230℃ for 2.5h, oligomers were obtained with a number average molecular weight of 3125g / mol.

[0065] After mixing the oligomer with 3.04 g of reinforcing agent B, the reaction pressure was gradually reduced to 50 PaA, and the mixture was reacted at 240 °C for 3.5 h to obtain a biodegradable copolyester with a number-average molecular weight of 2.9 × 10⁻⁶. 4 g / mol, melt index is 8.0 g / 10 min;

[0066] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3250mN, a dart impact strength of 266g, a tensile strength of 54MPa, and a tensile modulus of 132MPa.

[0067]

Example 3

[0068] 1) Mix 292g adipic acid, 332g terephthalic acid, 405g 1,4-butanediol, and 159g diethylene glycol, then add 3.56g tetraisopropyl titanate. After reacting at 210℃ for 3h, an oligomer is obtained with a number average molecular weight of 3308g / mol.

[0069] After mixing the oligomer with 5.94 g of reinforcing agent C, the reaction pressure was gradually reduced to 100 PaA, and the mixture was reacted at 250 °C for 3 h to obtain a biodegradable copolyester with a number-average molecular weight of 3.2 × 10⁻⁶. 4 g / mol, melt index is 7.6 g / 10 min;

[0070] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3641mN, a dart impact strength of 283g, a tensile strength of 57MPa, and a tensile modulus of 146MPa.

[0071]

Example 4

[0072] 1) Mix 350.4g adipic acid, 332g terephthalic acid, 538.6g 1,4-butanediol, and 158.6g diethylene glycol, then add 5.52g tetraisooctyl titanate. After reacting at 190℃ for 3h, an oligomer is obtained with a number average molecular weight of 3650g / mol.

[0073] After mixing the oligomer with 9.66 g of reinforcing agent A, the reaction pressure was gradually reduced to 200 PaA, and the mixture was reacted at 260 °C for 3 h to obtain a biodegradable copolyester with a number-average molecular weight of 4.3 × 10⁻⁶. 4 g / mol, melt index is 4.2 g / 10 min;

[0074] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3967mN, a dart impact strength of 325g, a tensile strength of 59MPa, and a tensile modulus of 158MPa.

[0075]

Example 5

[0076] 1) Mix 438g adipic acid, 332g terephthalic acid, 600g 1,4-butanediol, and 353.3g diethylene glycol, then add 8.62g tetrabutyl titanate. After reacting at 170℃ for 3h, an oligomer is obtained with a number average molecular weight of 3561g / mol.

[0077] After mixing the oligomer with 17.23 g of reinforcing agent A, the reaction pressure was gradually reduced to 50 PaA, and the mixture was reacted at 235 °C for 3.5 h to obtain a biodegradable copolyester with a number-average molecular weight of 4.6 × 10⁻⁶. 4 g / mol, melt index is 3.9 g / 10 min;

[0078] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film machine temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 4113mN, a dart impact strength of 339g, a tensile strength of 50MPa, and a tensile modulus of 115MPa.

[0079]

Example 6

[0080] 1) Mix 438g adipic acid, 332g terephthalic acid, 600g 1,4-butanediol, and 353.3g diethylene glycol, then add 5.17g tetrabutyl titanate. After reacting at 190℃ for 2h, an oligomer is obtained with a number-average molecular weight of 3822g / mol.

[0081] After mixing the oligomer with 1.72 g of reinforcing agent A, the reaction pressure was gradually reduced to 50 PaA, and the mixture was reacted at 235 °C for 3.5 h to obtain a biodegradable copolyester with a number-average molecular weight of 3.8 × 10⁻⁶. 4 g / mol, melt index is 6.2 g / 10 min;

[0082] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3122mN, a dart impact strength of 261g, a tensile strength of 52MPa, and a tensile modulus of 104MPa.

[0083]

Example 7

[0084] 1) Mix 438g adipic acid, 332g terephthalic acid, 600g 1,4-butanediol, and 353.3g diethylene glycol, then add 4.46g tetrabutyl titanate. After reacting at 190℃ for 2h, an oligomer is obtained with a number-average molecular weight of 3784g / mol.

[0085] After mixing the oligomer with 7.43 g of reinforcing agent A, the reaction pressure was gradually reduced to 50 PaA, and the mixture was reacted at 235 °C for 3.5 h to obtain a biodegradable copolyester with a number-average molecular weight of 4.0 × 10⁻⁶. 4 g / mol, melt index is 4.5 g / 10 min;

[0086] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film machine temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3509mN, a dart impact strength of 288g, a tensile strength of 55MPa, and a tensile modulus of 108MPa.

[0087]

Example 8

[0088] 1) Mix 438g adipic acid, 332g terephthalic acid, 600g 1,4-butanediol, and 353.3g diethylene glycol, then add 4.46g tetrabutyl titanate. After reacting at 190℃ for 2h, an oligomer is obtained with a number-average molecular weight of 3802g / mol.

[0089] After mixing the oligomer with 7.43 g of reinforcing agent A, the reaction pressure was gradually reduced to 50 PaA, and the mixture was reacted at 235 °C for 3.5 h to obtain a biodegradable copolyester with a number-average molecular weight of 4.1 × 10⁻⁶. 4 g / mol, melt index is 4.4 g / 10 min;

[0090] 600g of copolyester was thoroughly blended with 290g of 3000-mesh calcium carbonate, 50g of polylactic acid, 10g of oleamide, and 10g of isoflavone diisocyanate, and then extruded (extruder temperature 180℃, speed 300rpm), followed by blown film blowing (blown film machine temperature 170℃, traction speed 30m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 3305mN, a dart impact strength of 271g, a tensile strength of 53MPa, and a tensile modulus of 103MPa.

[0091] Comparative Example 1

[0092] 1) Mix 438g adipic acid, 332g terephthalic acid, 600g 1,4-butanediol, and 353.3g diethylene glycol, then add 4.46g tetrabutyl titanate. After reacting at 190℃ for 2h, an oligomer is obtained with a number-average molecular weight of 3815g / mol.

[0093] Without adding reinforcing agents, the reaction pressure was gradually reduced to 50 PaA, and the oligomers were reacted at 235°C for 3.5 hours to obtain a biodegradable copolyester with a number-average molecular weight of 3.1 × 10⁻⁶. 4 g / mol, melt index is 7.7 g / 10 min;

[0094] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 2855mN, a dart impact strength of 230g, a tensile strength of 45MPa, and a tensile modulus of 87MPa.

[0095] Comparative Example 2

[0096] 1) Mix 438g adipic acid, 332g terephthalic acid, 600g 1,4-butanediol, and 353.3g diethylene glycol, then add 4.46g tetrabutyl titanate. After reacting at 190℃ for 2h, an oligomer is obtained with a number-average molecular weight of 3796g / mol.

[0097] After mixing the oligomer with 29.7 g of reinforcing agent A, the reaction pressure was gradually reduced to 50 PaA, and the mixture was reacted at 235 °C for 3.5 h to obtain a biodegradable copolyester with a number-average molecular weight of 6.2 × 10⁻⁶. 4 g / mol, melt index is 0.8 g / 10 min;

[0098] 630g of copolyester was thoroughly blended with 300g of 3000-mesh calcium carbonate, 50g of polylactic acid, 20g of erucamide, and 10g of hexamethylene diisocyanate, and then extruded (extruder temperature 170℃, speed 500rpm), followed by blown film blowing (blown film temperature 165℃, traction speed 20m / min) to obtain a biodegradable film. The film was tested and found to have a tear strength of 4593mN, a dart impact strength of 262g, a tensile strength of 37MPa, and a tensile modulus of 58MPa.

[0099] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a tear-resistant, biodegradable copolyester, characterized in that, Includes the following steps: 1) Adipic acid, terephthalic acid, 1,4-butanediol, and diethylene glycol are mixed and polymerized to obtain oligomers; 2) Mix the oligomer with the reinforcing agent and carry out a polycondensation reaction to obtain a biodegradable copolyester.

2. The preparation method according to claim 1, characterized in that, In step 1), the ratio of the total molar amount of 1,4-butanediol and diethylene glycol to the total molar amount of adipic acid and terephthalic acid is 1.1-2.0:1.

0. Preferably, in step 1), the molar ratio of 1,4-butanediol to diethylene glycol is 1.0-4.0:1.0; Preferably, the molar ratio of adipic acid to terephthalic acid is 0.5-1.5:1.

0.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1), the reaction temperature is 170-250℃, and the reaction time is 1-5 hours. Preferably, in step 1), the number-average molecular weight of the oligomer is 500-4000 g / mol; Preferably, in step 1), a catalyst is also added. Preferably, the amount of catalyst added is 0.1%-0.5% of the total mass of the reaction raw materials in step 1). Preferably, in step 1), the catalyst is a titanium-based catalyst, preferably a titanate ester, which can be selected from any one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, tetrabutyl titanate, and tetraisooctyl titanate.

4. The preparation method according to any one of claims 1-3, characterized in that, In step 2), the mass of the reinforcing agent added is 0.1%-1.0% of the total mass of the raw materials; Preferably, in step 2), the reinforcing agent is a glycidyl polyol amine; In step 2), the polycondensation reaction pressure is 10-500 Pa, the reaction temperature is 220-280 ℃, and the reaction time is 1-5 h.

5. The preparation method according to any one of claims 1-4, characterized in that, The glycidyl polyol amine was prepared by reacting glycidyl ether and polyol amine. Preferably, the glycidyl ether comprises one or more of 1,4-butanediol diglycidyl ether, glycerol triglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether, with 1,4-butanediol diglycidyl ether being the most preferred. Preferably, the polyol amine includes one or more of diethanolamine, N-methyldiethanolamine, triethanolamine, triisopropanolamine, diisopropanolamine, and N-butyldiethanolamine, with diethanolamine being the most preferred.

6. The preparation method according to any one of claims 1-5, characterized in that, The reaction between the glycidyl ether and the polyol amine is carried out in a solvent, and the amount of solvent added is 5-10 times the mass of the glycidyl ether. Preferably, the solvent is a diol, including one or more of ethylene glycol, 1,4-butanediol, and diethylene glycol, with 1,4-butanediol being the most preferred. Preferably, the mass ratio of the glycidyl ether to the polyol amine is 1:1-3; Preferably, the reaction temperature of the glycidyl ether with the polyol amine is 50-60°C, and the reaction time is 2-5 hours.

7. The application of the copolyester prepared by the preparation method according to any one of claims 1-6, for the preparation of biodegradable membranes.

8. A biodegradable membrane comprising the following raw materials in parts by weight: 50-70 parts copolyester 20-30 parts calcium carbonate 5-10 parts of polylactic acid 0-2 parts of opening agent 0-1 part compatibilizer; The copolyester is a copolyester prepared by any one of claims 1-7.

9. The biodegradable membrane according to claim 8, characterized in that, The fineness of calcium carbonate is 1000-8000 mesh, preferably 3000-6000 mesh; Preferably, the opening agent can be selected from one or more of stearamide, erucamide, and oleamide, with erucamide being preferred; Preferably, the compatibilizer may be selected from one or more of hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and isoflurone diisocyanate, with hexamethylene diisocyanate being the most preferred.

10. The method for preparing the biodegradable membrane according to claim 8 or 9, characterized in that, The copolyester is thoroughly blended with calcium carbonate, polylactic acid, optional opening agent and optional compatibilizer, and then extruded and blown into a film to obtain a biodegradable film. Preferably, the extrusion temperature is 150-200℃ and the extrusion speed is 200-500 rpm; Preferably, the blown film is made using a blown film machine, with a screw temperature of 150-200℃ and a traction speed of 10-30m / min; Preferably, the number-average molecular weight of the biodegradable membrane is 2 × 10⁻⁶. 5 -8×10 5 The melt index is 1-10 g / 10 min at 190℃ and 2.16 kg.